According to Plueddemann, in the chapter on silylating agents in "Encyclopedia of Chemical Technology", 3rd edition, volume 20, page 962 et seq., silylation is the displacement of active hydrogen from an organic molecule by a silyl group. Plueddemann further states that "The active hydrogen is usually OH, NH, or SH, and the silylating agent is usually a trimethylsilyl halide or a nitrogen-functional compound. A mixture of silylating agents may be used; a mixture of trimethylchlorosilane and hexamethyldisilazane is more reactive than either reagent alone, and the by-products combine to form neutral ammonium chloride."
Thus, what Plueddemann has described is what those skilled in the art regard as the "normal way" to silylate organic molecules using reactive silanes.
It has been beneficial to industry to have this approach available to alter organic molecules to achieve certain new molecules. See, for example, Poole, C. F., Recent Advances in Silylation of Organic Compounds for Gas Chromatography, Chapter 4, "Handbook of Derivatives for Chromatography", K. Blau and G. King, Heyden, London, 1977, p. 152-200. Those skilled in the art have extrapolated silylation of organic molecules to silylation of inorganic molecules and materials as well. For example, it is known that silicas, used as fillers for compounded rubbers, could be treated with reactive silanes such as trimethylchlorosilane and/or hexamethyldisilazane to place trimethylsilyl groups on the surface of such silicas. This treatment arises through the reaction of the hydroxyls on the silica with the reactive silanes. See, for example, Hertl, W. and Hair, M. L., "Reaction of Hexamethyldisilazane with Silica", J. of Phys. Chem., Volume 75, No. 14, 1971 and Chmieloweic, J. and Marrow, B. A., "Alkylation of Silica Surfaces", J. of Coll. and Inter. Sci., Volume 94, No. 2, August 1983 and Boksanyi, L., Liardon, O. and Kovats, E., Advances in Coll. and Inter. Sci., 6 (1976), p. 95-137.
Porous support materials used in liquid or thin layer chromatography applications also benefit by silylation techniques. Such materials have a very large surface area within their porous interior, so that the exterior surface accounts for less than one percent of the total surface area. Such materials can be in either particulate or non-particulate forms (e.g., coatings). It is common in this art to use reactive silanes to treat such materials to remove accessible reactive hydroxyl groups on the entire surface including that of the porous interior to improve the chromatographic properties of polar molecules. See, for example, L. R. Snyder and J. J. Kirkland, Introduction to Modern Liquid Chromatography, 2nd edition, Wiley-Interscience, N.Y. 1979.
A more significant advance in the silylation art came about by the use of reactive silanes which also contained organofunctional groups to silylate surfaces. The desired result was to create a material having a novel end-use which was dependent on the type of organofunctional group included in the silylating silane. For example, in U.S. Pat. No. 4,379,931, issued on Apr. 12, 1983, Plueddemann used unique reactive silanes, for example ##STR1## to treat various particulate materials which were then used to extract metal ions from solution.
For most of the practical applications known in the prior art, the preferred mode of silylation is that which is carried out in solution. There are, however, some silylation applications wherein the silylation reaction is carried out from the vapor phase. It can be concluded therefore that it is generally known in the art to use various reactive silanes to react with hydroxyls on the surfaces of various materials.